CEMENT  MATERIALS  OF  THE  VALLEY  OF  VIRGINIA. 
By  R.  S.  Bassler. 
CEMENT-MAKING  ROCKS. 
For  many  years  the  argillaceous  Trenton  limestones  of  the  Lehigh 
district  of  Pennsylvania  have  furnished  the  raw  material  for  the 
manufacture  of  the  greater  part  of  the  Portland  cement  output  of 
the  United  States.  Because  of  this  enormous  output  the  argilla- 
ceous limestones  of  this  relatively  small  district  have  assumed  great 
economic  importance,  and  the  occurrence  of  the  same  rock  in  adjoin- 
ing States  is  of  great  interest  to  cement  manufacturers. 
In  the  early  part  of  the  field  season  of  1904  the  writer  spent  six 
weeks  in  the  Lehigh  and  Lebanon  valleys  of  Pennsylvania  in  a  gen- 
eral study  of  the  paleontology  and  stratigraphy  of  the  Ordovician 
strata,  but  particularly  in  mapping  the  distribution  of  the  Trenton 
limestone  or  cement  rock.  Later  in  the  season  about  three  weeks 
were  devoted  to  similar  work  in  the  southern  half  of  the  Valley  of 
Virginia.  The  following  preliminary  report  and  accompanying 
maps  are  based  largely  upon  this  latter  field  work,  but  in  their 
preparation  free  use  has  been  made  of  the  Staunton  folio,a  by  N.  H. 
Darton,  and  of  an  article  by  Charles  Catlett  entitled  "  Cement  re- 
sources of  the  Valley  of  Virginia."  h  Acknowledgements  are  also 
due  to  Prof.  H.  D.  Campbell,  of  Washington  and  Lee  University,  for 
the  use  of  manuscript  geologic  maps  prepared  by  him  covering  the 
region  about  Lexington  and  Natural  Bridge,  Va.  Mr.  Catlett  has 
also  kindly  allowed  the  writer  to  make  use  of  notes  and  preliminary 
analyses  of  the  rocks  in  the  vicinity  of  Harrisonburg  and  Staun- 
ton, Va. 
In  the  present  report  only  thai  p;irt  of  the  valley  lying  between 
Woodstock,  in  Shenandoah  County,  on  the  north  and  Natural  Bridge, 
in  Rockbridge  County,  on  the  south  is  considered. 
"Geologic  Atlas  U.  S.,  folio  14.  IT.  S.  Geol.  Survey,  1894. 
6  Bull.  U.  S.  Geol.  Survey  No.  225,  11)04,  pp.  457-401. 
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